Southern California -- this just in

Some L.A. County mosquitoes test positive for West Nile virus

A fourth sampling of mosquitoes in L.A. County has tested positive for West Nile virus, with some of the hottest days of the year still to come, officials said Monday.

A sample of 42 mosquitoes from Rowland Heights recently came back positive for the virus, according to Truc Dever, a spokeswoman for the Greater Los Angeles County Vector Control District.

It was the first sign of activity in Rowland Heights, but mosquitoes from Silver Lake, Newhall and Encino have tested positive for the virus in the last month. Dever said the Rowland Heights sample was taken June 21.

“About this time of year, we start seeing more and more activity,” Dever said. “West Nile virus is endemic to California, it’s always going to be here.”

Dever said that even a tiny amount of water, like in a bottle cap, can be enough for a mosquito to lay its eggs. She clarified that although large numbers of mosquitoes are sampled, not all of them have to test positive to elicit a positive result.

Although many people are bitten by mosquitoes that carry West Nile virus, most do not know they have been exposed, public health officials say. Few people develop severe infections or even notice any symptoms, including fever, abdominal pain, nausea, diarrhea, headache, sore throat and a lack of appetite.

Routine testing of adult female mosquitoes in June at Modjeska Park in Anaheim also uncovered the virus in Orange County.

Dever said Northern California has seen a particular increase in virus activity, and she said that record-high temperatures this summer could bring “a proliferation of the mosquitoes' population” to Southern California as well.